Filament connection for electric lamps



April s, 1958 w. F. HODGE 2,830,217

FILAMENT CONNECTION FOR ELECTRIC LAMPS Filed June 15, 195s Inventor: William F. Hodge,

y 022$ His At ney United States Patent U FILAMENT CONNECTION non ELECTRIC LAMPS William F. Hodge, Lyndhurst, Ohio, assignor to General Electric Company, a corporation of New York Application June 15, 1955, Serial No. 515,712

1 Claim. (Cl. 313-274) My invention relates to electrical devices comprising a sealed bulb containing an incandescible coiled filament, such as electric incandescent lamps. More particularly, my invention relates to improvements in the joint structure by which the filament is connected to the current supply or lead-in conductors.

In devices of the aforesaid type, the general practice is to form the connection or joint by providing the ends of the lead-in wires with hooks which are clamped about the ends of the filament. Welded joints are also employed to a substantial extent. However, in certain applications such as those involving high wattages or certain types of metal or relatively large filament coils, the simplified hook clamp or welded type joints are not feasible. In such cases, various constructions have been proposed and used in commercial devices. However, they are usually of a somewhat complicated nature and therefore relatively expensive.

It is therefore a primary object of the present invention to provide a filament joint which is of simplified and inexpensive construction, and yet provides a reliable electrical and mechanical connection.

Briefly stated, in accordance with one aspect of my invention, I provide a filament joint wherein the lead-in wire is formed with a flattened end portion having a width slightly larger than the inside diameter of the filament coil and which is inserted into an end of the said coil to cause the coil to be distended so as to tightly grip the lead-in wire.

My invention will be better understood from the following description taken in conjunction with the accompanying drawing and its scope will be pointed out in the appended claim.

In the drawing, Fig. 1 is a side view of one form of electric lamp device embodying my invention;

Fig. 2 is a side View, on an enlarged scale, of portions of a lead-in conductor and filament connected together in accordance with my invention; and

Fig. 3 is a side view of a portion of the lead-in conductor illustrated in Fig. 2 as viewed with the wire rotated 90 degrees from its position in Fig. 2.

Referring to Fig. 1, the lamp illustrated therein is of the infrared generator type recently introduced on the market. It comprises an elongated tubular envelope 1 which may consist essentially of fused silica, such as clear crystal quartz, translucent sand quartz or a quartz-like glass such' as that commercially known as Vycor and containing approximately 96 percent silica. The envelope preferably contains a filling of rare gas such as argon, krypton, xenon, or mixtures thereof at a pressure of several hundred millimeters. A helically coiled tungsten wire filament 2 extends axially of the envelope, substantially throughout its length and is connected, under tension, at its opposite ends to lead-in conductors 3 hermetically sealed directly in flattened press or seal portions 4 of the quartz envelope. The conductors 3 are preferably formed of refractory metal such as molybdenum which is flattened throughout an intermediate portion 5 of its length to a thickness of between .0005 and .0010 inch. The filament 2 is supported at intermediate points along its length by a plurality of centrally perforated discs 6 preferably formed of tantalum.

In accordance with the present invention, the inner end 7 of each of the lead-in wires 3 is flattened, preferably to the configuration shown in Figs. 2 and 3. As shown in Fig. 3 the compressed or flattened portion 7 has a minimum thickness at a point 10 removed inwardly from the extremity of the wire and is tapered longitudinally in increasing thickness to the said extremity. As shown in Fig. 2, in a direction transverse to the direction of thickness shown in Fig. 3 and complementary thereto, the flattened portion '7 flares abruptly outward to a maximum width at the point 8 which is slightly larger than the inside diameter of the filament coil 2. The flattened portion then tapers downward toward the terminus of the wire to a width which is sufliciently small to easily enter the end of the filament coil. The length of the flattened portion 7 is such that a suitable taper is obtained to provide ease of entry of the flattened portion into the coil.

The flattened end of the lead-in wire 3 may be assembled with the filament coil 2 by screwing it thereinto or by simply thrusting it into the coil. The coil is thereby slightly distended at the widest part 8 of the conductor 3 to form a tight connection therebetween, and a portion of one turn thereof is caught behind the shoulder 9. The parts are therefore readily assembled by a simple operation and the resulting joint has proved to be highly effective both mechanically and electrically.

The flattening of the lead-in conductor 3 is performed with a pair of suitably shaped jaws. The jaws are preferably mounted in a pneumatically operated press inasmuch as the hammer-like action of a punch press was found to result in a large number of cracked wires. It is also highly desirable to provide the small radius indicated at 10 in Fig. 3 in order to avoid cracking the molybdenum wire.

In a specific embodiment for infrared lamps of 500 and 1000 watt rating, with a lead-in wire of .030 inch diameter and a filament coilof about .045 inch-inside diameter, good results are attained when the end of the wire is flattened to a width, at the point 8, of approximately .047 inch; a width at the terminus of the flat 7, as seen in Fig. 2, of about .035 inch; and with an overall length of the flattened portion 7 of about inch.

What I claim as new and desire to secure by Letters Patent of the United States is:

In an electrical device comprising a sealed bulb containing an incandescible coiled filament, a lead-in wire connected to said filament by a joint structure wherein the lead-in wire is of smaller diameter than the inside diameter of the filament coil, said lead-in wire being provided with a compressed end portion having a minimum thickness at a point removed inwardly from the extremity of the wire and tapering longitudinally in increasing thickness to the said extremity and having a complementary maximum width at said point of minimum thickness flaring abrupting outward in a direction transverse to the direction of said thickness to form a shoulder and tapering longitudinally in decreasing Width to said extremity, the said maximum width slightly exceeding the coil inside diameter, said compressed end portion being disposed wholly within an end of said coil whereby the coil is locally distended and firmly grips the lead-in wire at its point of maximum width with a portion of a turn of the coil caught behind said shoulder.

References Cited in the file of this patent UNITED STATES PATENTS 

